1. Field of the Invention
The field of the invention is computer equipment for linking a plurality of machine or process controllers in a factory automation network.
2. Description of the Background Art
In factory automation, more complex functions could be performed and coordinated if the programmable or computerized machines presently used to control mechanical equipment could be connected in a network with each other and with higher level supervisory computers. A network would allow the "reconfiguring" of the assembly line by communicating new programs to the programmable systems from a central computer. The network would also provide numerous monitoring and report functions at designated locations and these would provide managers with information to further improve efficiency of manufacturing operations.
Many programmable tools, instruments and control systems are now installed in industry, however, many of these programmable machines cannot communicate with each other. It has been estimated that to establish such communication through custom hardware and software interfaces may account for up to 50 percent of the cost of factory automation.
In anticipation of acquiring a large amount of programmable equipment to automate its factories, certain large manufacturers have established MAP (Manufacturing Automation Protocol). MAP is a seven-layer communications specification for interconnection of general purpose mainframe computer equipment to specialized computer controllers that control individual machines or processes. The MAP standard is not complete at all seven of its layers and is still in the process of development. The MAP standard is also being implemented in phases as equipment has not been available to meet all of the MAP specifications, and new equipment is being designed to provide the MAP-networking capability.
Demonstrations of early phase MAP networks have pointed to possible problems that have not as yet been addressed or solved. One problem has been the time involved in downloading programs and data from supervisory computers to stations on the factory floor. Even if computers are able communicate, communication networks can develop bottlenecks where too many messages are required to accomplish a certain task, where redundant data is being communicated or where too many protocol translations are required. Another problem has been the need for central computers to recompile entire application programs to implement simple changes in data tables or in the arrangement of discrete devices on equipment being controlled by station-level controllers.
When an application program is written on a central computer, items of data or variables stored at station level are represented by certain labels rather than specific addresses or locations in memory where they will be found. When the application program is compiled, the items of data in the program are assigned addresses in the memory of the central computer.
At the stations some data variables are related to the physical connection of devices on the controlled machine. When an additional device, such as a photoelectric sensor, is connected the programmable controller, a new data item is created in the memory of the programmable controller. Other new data items such as timing variables may be created in the memory of the programmable controller without connecting additional devices to the controller.
In one MAP demonstration, the incorporation of the new data item or variable at the station level required a recompilation of application programs and data files at the level of the central computer. In this instance recompilation was required to relate the address or location of the new variable at the station level to an address or location in the data files of the central computer.
Although standardization of communication network standards is an important development, reaching the goals of factory automation will also require innovative solutions such as those offered by the present invention.